On a new algorithm for time step integration of nonlinear systems

A new implicit algorithm for time step integration of finite element structural dynamic equations is presented. Convergence, stability and numerical damping properties are discussed. Due to the way nonlinear structural behavior is taken into account, the algorithm is expected to compare favorably with existing ones. Some simple numerical results are presented. A related explicit algorithm is also derived and shortly discussed

A cell-based smoothed finite element method for kinematic limit analysis

This paper presents a new numerical procedure for kinematic limit analysis problems, which incorporates the cell-based smoothed finite element method with second-order cone programming. The application of a strain smoothing technique to the standard displacement finite element both rules out volumetric locking and also results in an efficient method that can provide accurate solutions with minimal computational effort. The non-smooth optimization problem is formulated as a problem of minimizing a sum of Euclidean norms, ensuring that the resulting optimization problem can be solved by an efficient second-order cone programming algorithm. Plane stress and plane strain problems governed by the von Mises criterion are considered, but extensions to problems with other yield criteria having a similar conic quadratic form or 3D problems can be envisaged

Homogenized rigid-plastic model for masonry walls subjected to impact

A simple rigid-plastic homogenization model for the analysis of masonry structures subjected to out-of-plane impact loads is presented. The objective is to propose a model characterized by a few material parameters, numerically inexpensive and very stable. Bricks and mortar joints are assumed rigid perfectly plastic and obeying an associated flow rule. In order to take into account the effect of brickwork texture, out-of-plane anisotropic masonry failure surfaces are obtained by means of a limit analysis approach, in which the unit cell is subdivided into a fixed number of sub-domains and layers along the thickness. A polynomial representation of micro-stress tensor components is utilized inside each sub-domain, assuring both stress tensor admissibility on a regular grid of points and continuity of the stress vector at the interfaces between contiguous sub-domains. Limited strength (frictional failure with compressive cap and tension cutoff) of brick-mortar interfaces is also considered in the model, thus allowing the reproduction of elementary cell failures due to the possible insufficient resistance of the bond between units and joints. Triangular Kirchhoff-Love elements with linear interpolation of the displacement field and constant moment within each element are used at a structural level. In this framework, a simple quadratic programming problem is obtained to analyze entire walls subjected to impacts. In order to test the capabilities of the approach proposed, two examples of technical interest are discussed, namely a running bond masonry wall constrained at three edges and subjected to a point impact load and a masonry square plate constrained at four edges and subjected to a distributed dynamic pressure simulating an air-blast. Only for the first example, numerical and experimental data are available, whereas for the second example insufficient information is at disposal from the literature. Comparisons with standard elastic-plastic procedures conducted by means of commercial FE codes are also provided. Despite the obvious approximations and limitations connected to the utilization of a rigid-plastic model for masonry, the approach proposed seems able to provide results in agreement with alternative expensive numerical elasto-plastic approaches, but requiring only negligible processing time. Therefore, the proposed simple tool can be used (in addition to more sophisticated but expensive non-linear procedures) by practitioners to have a fast estimation of masonry behavior subjected to impact

Homogenization and seismic assessment : review and recent trends

The mechanics of masonry structures has been for long underdeveloped in comparison with other fields of knowledge. Presently, non-linear analysis is a popular field in masonry research and advanced computer codes are available for researchers and practitioners. The chapter presents a discussion of masonry behaviour and clarifies how to obtain the non-linear data required by the computations. The chapter also addresses different homogenisation techniques available in the literature in the linear and rigid-plastic case, aiming at defining a catalogue and at discussing the advantages and disadvantages of the different approaches. Special attention is given to stress assumed models based either on a polynomial expansion of the micro-stress field or in the discretization of the unit cell by means of a few constant stress finite elements CST with joints reduced to interfaces. Finally, the aspects of seismic assessment are presented and case studies involving the use of macro-block analysis, static (pushover) analysis and time integration analysis are discussed.(undefined

Leaving the Planar Universe

A computer program is presented which generates realistic images of planned buildings embedded in their future environment through photomontage. The planar universe of conventional photomontaging is extended to three dimensions. During an interactive preprocessing step, a three- dimensional model of the building's environment is created: Geometrical data is retrieved photogrammetrically from a number of site photographs. Atmospheric parameters and the relative weights of the components of natural daylight are also retrieved from the photographs. The final image, combining the artificial model of the building and the photographs of its surroundings, is rendered by an extended ray-tracing algorithm in three-dimensional object space